Self-Plasticization of PVC Materials via Chemical Modification of

Research Article pubs.acs.org/journal/ascecg

Self-Plasticization of PVC Materials via Chemical Modification of Mannich Base of Cardanol Butyl Ether Puyou Jia,† Lihong Hu,†,‡ Qianqian Shang,† Rui Wang,§ Meng Zhang,*,†,‡ and Yonghong Zhou*,† †

National Engineering Lab for Biomass Chemical Utilization, Key Lab on Forest Chemical Engineering, State Forestry Administration, and Key Lab of Biomass Energy and Materials, Institute of Chemical Industry of Forest Products, Chinese Academy of Forestry (CAF), Jiangsu Province, 16 Suojin North Road, Nanjing 210042, P. R. China ‡ Institute of Forest New Technology, Chinese Academy of Forestry, Dongxiaofu-1 Xiangshan Road, Beijing 100091, P. R. China § College of Materials Science and Engineering, Nanjing Forestry University, 159 Longpan Road, Nanjing 210037, P. R. China S Supporting Information *

ABSTRACT: The internally plasticized PVC materials by displacement of chlorine with mannich base of cardanol butyl ether, that is, the covalent attachment of the cardanol-based internal plasticizer to the PVC matrix, is descried for the first time. The chemical structure and properties of cardanol-based internal plasticizer and internally plasticized PVC materials was characterized. The results showed that the Tg of selfplasticization PVC material decreased from 85.6 to 49.3 °C when chlorine atoms in PVC were substituted with mannich base of cardanol butyl ether, tensile strength decreased from 30.33 to 18.86 MPa, and the elongation at break increased from 180.37% to 357.20%, which illustrated that mannich base of cardanol butyl ether played internally plasticized effect on PVC. The internal plasticization mechanism was also studied. Self-plasticization PVC films showed no migration in n-hexane, but 15.7% of DOP leached from the DOP/PVC system into n-hexane. The PVC materials were expected to be commercial application in producing food packing, toys, and medical devices with high requirements in migration resistance. KEYWORDS: Cardanol, Polyvinyl chloride, Manihi reaction, Plasticization, Glass transition temperature

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INTRODUCTION Polyvinyl chloride (PVC) is the third most widely used polymer around the world, only behind polyethylene and polypropylene.1 PVC production of China in 2016 reached 1.33 million tons and is expected to continue to grow. PVC is a rigid and brittle flour. In order to obtain flexile and malleable polymer products, a large amount of plasticizer is blended with the polymer. The most frequently used plasticizer is phthalate ester, which accounted for 70% of the global plasticizer demand in 2014.2 However, many researchers reported that phthalate esters are easy to migrate from the polymer matrix into the environment during processing and using with increasing time, which decreased the service life of polymer products, as well as potential toxicity to the human body.3−8 Several strategies were investigated to avoid the migration of phthalate plasticizers; the most widely studied method is to develop alternative plasticizers such as epoxidized vegetable oil,9−12 polymer plasticizer,13−16 polyol ester,17 and phosphate plasticizer.18,19 Although these alternative plasticizers suppress the migration from PVC products in a certain degree, the small molecule plasticizers (epoxidized vegetable oil, polyol ester, and phosphate plasticizer) will migrate from PVC products with increasing time. The polymer plasticizers with low plasticization © 2017 American Chemical Society

effect cannot be used as a main plasticizer. Recently, some researchers focused on the method of covalent attachment of plasticizer onto the PVC chains to prevent the plasticizer from migrating. PVC materials were plasticized in this way by increasing the distance of PVC chains and decreasing the interaction force, further promoting the PVC chains as moveable. The internal plasticization method by displacement of chlorine with phthalate-based thiol additives obtained good plasticization efficiency, which was described by Navarro et al.20 The chemical structure of the polymer is shown in Figure 1, though the modified PVC materials exhibited zero migration, and the flexibility of the materials was reduced compared with PVC/phthalate systems. Earla et al.21,22 reported the covalent attachment of phthalate derivatives onto the PVC chains via click chemistry. Figure 1 showed the chemical structure of internally plasticized PVC materials. The internally plasticized PVC materials gave lower Tg than the PVC/diethylhexyl phthalate (DEHP) system, indicating the plasticization strategy was successful. Click chemistry opens new gates for preparing Received: March 24, 2017 Revised: June 21, 2017 Published: June 29, 2017 6665

DOI: 10.1021/acssuschemeng.7b00900 ACS Sustainable Chem. Eng. 2017, 5, 6665−6673

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ACS Sustainable Chemistry & Engineering

anthracis spores.32 The displacement of chlorine with aminated derivatives was usually used to modify PVC surfaces for preparing functional ultrafiltration membranes with improved antifouling properties, which was reported by Jiang et al.33−35 Covalent immobilization of trypsin and chymotrypsin onto aminated-PVC microspheres was also descried by Li et al.36 However, the displacement of chlorine with amianted derivatives via single reaction for plasticizing PVC materials has never reported. In the present work, we reported the development of a kind of mannich base of cardanol butyl ether, which was used as a novel biobased and nonmigration plasticizer for self-plasticization PVC materials with excellent migration resistance. Mannich base of cardanol butyl ether was synthesized from cardanol via substitution reaction and manihi reaction. Then the self-plasticization PVC materials were obtained by displacement of chlorine with mannich base of cardanol butyl ether, which was used as an internal plasticizer. The structure of mannich base of cardanol butyl ether and self-plasticization PVC materials was detected. The glass transition temperature (Tg) and tensile tests were used to study the plasticizing effect. The thermal stability, migration resistance, and internal mechanism were also investigated. The self-plasticization PVC materials exhibited better flexibility than that of PVC and presented excellent migration resistance compared with that of the PVC/DOP system. The study opens new gates for preparing added value products using cardanol.

Figure 1. Internally plasticized PVC materials.

internally plasticized PVC materials. In addition, some new internal plasticizers such as propargyl ether cardanol,23 propargyl ether triethyl citrate,24 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) containing castor oil based derivative,25 and hyperbranched polyglycerol26 were reported in succession, just as seen from Figure 1. Yang et al. developed a biobased cardanol-based plasticizer, which covalently linked to the PVC chain via a click reaction. The modified PVC materials showed low Tg, excellent thermal stability, and near-zero migration comparing with PVC/DOP blends. Lee et al. further reported the internal plasticization strategy; hyperbranched polyglycerol was click grafted on the PVC chains in the same way. Our group developed two kinds of biobased internal plasticizers: propargyl ether triethyl citrate and DOPO containing a castor oil based derivative, which were covalently attached on the PVC chain and achieved excellent plasticization efficiency. However, the click chemistry strategy was usually carried on with copper ion catalyst such as cuprous bromide, cuprous iodide, and blue copperas. These copper ion catalysts were hard to remove, which limited the PVC materials further application. Therefore, more attention was paid to the catalysts-free strategy. Several synthetic strategies were attempted to substitute chlorine with trichlorotriazine-based sodium thiolates with different aliphatic chains via one-pot procedure, which was reported by Navarro et al.27,28 The application of inexpensive starting materials such as trichlorotriazine and copper ion catalyst-free extended the application of the method in internally plasticizing PVC materials. However, the separation and purification process of products in a one-pot procedure was complicated. The displacement of chlorine with aminated derivatives via single reaction is similar to the click reaction and one-pot procedure for preparing internally plasticized PVC materials but without catalyst and impurities. Recently, the studies of displacement of chlorine with aminated derivatives have been investigated and used in removing heavy metal ions of industrial wastewater, Knoevenagel condensation as catalyzer, and preparing ultrafiltration membranes. Ahamed et al.29 reported the modified PVC polymers with aminated castor oil, which was used to remove heavy metal ions of industrial wastewater. The displacement of chlorine with tetraethylenepentamine and 2-aminoethanol was used to prepare catalysts for the Knoevenagel condensation and Heck reactions, which were reported by Dong et al. and Huang et al.,30,31 respectively. The aminated-PVC (PVC-NH2) coated quartz crystal microbalance (QCM) immunosensor was also used to detect Bacillus

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EXPERIMENTAL SECTION

Materials. Butyl chloride, tetrahydrofuran (THF), N,N-dimethylformamide (DMF), methanol, potassium carbonate, diethylenetriamine, hydrochloric acid, formaldehyde solution (37%), silver nitrate, ammonium thiocyanate, ammonium ferric sulfate, sodium hydroxide, and potassium chromate were kindly provided by Nanjing Chemical Reagent Co., Ltd. All raw materials are analytical grade and used without further purification. Cardanol (99%, acid value 5.5−6.6, iodine value 210−250) was provided by Jining Hengtai Chemical Co., Ltd. Polyvinyl chloride (PVC) was supplied by Hanwha (KM-31, South Korea). Synthesis of Cardanol Butyl Ether. Cardanol (302 g, 1 mol), butyl chloride (97.2 g, 1.05 mol), and 200 mL of DMF was mixed in a three-necked round-bottom, which was equipped with a mechanical stirrer, condenser pipe, and nitrogen tube at room temperature. Potassium carbonate (138.2 g, 1 mol) was added to the solution gradually. Then the mixture was stirred at 120 °C for 6 h with protection of nitrogen to finish the reaction. Potassium carbonate was filtered. Oxblood red cardanol butyl ether with productivity of 97% was obtained after washing with distilled water and drying with vacuum distillation. Figure 2 shows the synthetic route. Synthesis of Mannich Base of Cardanol Butyl Ether. Cardanol butyl ether (35.8 g, 0.1 mol) and diethylenetriamine (10.3 g, 0.1 mol) were mixed in a three-necked round-bottom, and then 37 wt % formaldehyde (8.1 g) and 10 mL of hydrochloric acid were added to the solution, which was equipped with a mechanical stirrer, condenser pipe, and thermometer. The formaldehyde was dropped in the solution in 20 min. The mixture was stirred at 90 °C for 4 h. After that, the temperature was raised to 120 °C to remove water. Then the mannich base of cardanol butyl ether was obtained, with an amine value of 220 mg/g. Synthesis of Self-Plasticization PVC Materials. A total of 5 g of PVC and a certain amount of mannich base of cardanol butyl ether was dissolved in 80 mL of DMF. The mixture was stirred at 80 °C for 2 h. Then the self-plasticization PVC material was obtained after washing with 10 wt % aqueous methanol solution and drying in an electrothermal blowing drybox at 60 °C. The composition of reactants is showed in Table S1. 6666


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Machine (MTS Instrument Crop., China) at a strain rate of 20 mm/ min with a 50 N static tension. The leaching tests were performed and were carried out according to ASTM D5227. PVC and self-plasticization PVC films after weighting were immersed in n-hexane at 50 °C for 2 h. These PVC and self-plasticization PVC films were dried and reweighed. The extraction loss was calculated according to the equation: degree of migration = [(W1 − W2)/W1)] × 100, where W1 = initial weight of tested specimen and W2 = final weight of test PVC films.

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RESULTS AND DISCUSSION Mannich reaction has bright prospects in the area of organic synthesis. Many compounds with structural complexity and diversity can be obtained via mannich reaction from simple and readily available starting materials without separation of intermediates. The FT-IR spectra of the cardanol, cardanol butyl ether, and mannich base of cardanol butyl ether are monitored and shown in Figure S1. The strong and characteristic absorption peaks were labeled in Figure S1. As seen from the FT-IR spectrum of cardanol, the strong and broad absorption peak is assigned to the stretch vibration of −OH groups. The absorption peak at 3007 cm−1 corresponds to the alkyne C−H stretch. The strong absorption peaks at 2924, 2853, and 1586 cm−1 are attributed to C−H, −C−H, and C−C bonds. The broad absorption at the range of 1454− 1152 cm−1 is assigned to the CC stretching mode of vibration from the benzene ring.37−40 The disappearance of the strong and broad absorption peak assigned to the stretch vibration of −OH groups in the FT-IR spectrum of cardanol butyl ether, with concomitant constants of other absorption peaks compared with that of cardanol, is indicative of the formation of the cardanol butyl ether.41 New absorption peaks at 3356 and 3292 cm−1 can be found in the FT-IR spectrum of mannich base of cardanol butyl ether, which respectively represent the primary and secondary amine N−H stretching vibrations. The peak at 1668 cm−1 is assigned to the rocking vibration of N−H. The absorption peak at 1041 cm−1 corresponds to the vibration of C−N, and the weak and broad peaks at 694 cm−1 are attributed to N−H twisting vibrations,41 which is indicative of the formation of the mannich base of cardanol butyl ether. The chemical structures of cardanol, cardanol butyl ether, and mannich base of cardanol butyl ether were detected by 1H NMR, and all of the peaks in the 1H NMR spectra were easily assigned, and no side products were observed, as shown in the 1 H NMR spectrum of cardanol (Figure S2). The peak at 0.94 ppm was attributed the protons of methyl groups on the long fatty acid chains. The strong peak at 1.36, 1.41, 2.09, 2.5, and 2.8 ppm was assigned to the protons of methylene groups.37−40 The signal at 5.41 ppm was assigned to protons of hydroxyl groups. The protons of olefin groups appeared at 5.44 ppm, and the signals of protons for benzene rings can be observed at 6.71, 6.82, and 7.18 ppm.39,40 Compared with the 1H NMR spectrum of cardanol butyl ether, new peaks appeared at 0.99, 1.77, 2.92, and 3.97 ppm, which were attributed to the protons of methyl and methylene groups derived from butyl chloride, respectively. In addition, the signal at 5.41 ppm disappeared, indicating that the cardanol butyl ether was obtained. As seen from the 1H NMR spectrum of mannich base of cardanol butyl ether, new signals appeared at 3.39, 3.48 and 6.32, 6.75 ppm, which were assigned to protons of methylene groups and the secondary amine derived from diethylenetriamine,41 indicating that the mannich reaction was finished.

Figure 2. Synthesis of mannich base of cardanol butyl ether and selfplasticization PVC materials. Preparation of Self-Plasticization PVC Films. A total of 5 g of self-plasticization PVC material was dissolved in 60 mL of THF. The mixture was stirred at 40 °C for 20 min until the solution presented transparent. After that, the solution was poured into a glass Petri dish (10 cm diameter), and the dried in a drying box at 60 °C for 24 h to completely remove residual THF. Then the PVC film with a thickness of approximately 0.1 mm was obtained. PVC film and 50 wt % DOP/ PVC system were obtained using the same method. Characterization. Fourier transform infrared (FT-IR) spectra of intermediate products and self-plasticization PVC materials were performed on a Nicolet iS10 FTIR (Nicolet Instrument Crop., USA) Fourier transformed infrared spectrophotometer. The spectra were acquired in the range of 4000 to 500 cm−1 at a resolution of 4 cm−1. Peaks were labeled in the spectra automatically via OMNIC software (Thermo Electron Corporation, U.S.A.). 1 H and 13C NMR spectra of intermediate products and selfplasticization PVC materials were performed on an AV-300 NMR spectrometer (Bruker Instrument Crop., Germany) at a frequency of 400 MHz. The process was carried out using CDCl3 as solvent and tetrametnylsilane (TMS) as an internal standard. The NMR data was processed using MestReNova software (Santiago de Compostela, Spain). Chlorine content of PVC and self-plasticization PVC materials were tested using Volhard method according to China National Standard GB/T 7139-2002 (plastic-vinyl chloride homopolymers and copolymers-determination of chlorine content). Weight-average molecular weight and dispersity of PVC and selfplasticization PVC materials were investigated on an Efficient gel permeation chromatograph (GPC) measurement made by Waters, USA at 30 °C (flow rate: 1 mL/min, column: mixed PL gel 300 × 718 mm, 25 μm) using HPLC-grade THF as solvent. PVC and selfplasticization PVC material were brought into THF solutions with a known concentration of 1−5 mg/mL. The thermogravimetric analysis (TGA) tests were carried out using a TG209F1 TGA thermal analysis instrument (Netzsch Instrument Crop., Germany) in N2 atmosphere (50 mL/min) at a heating rate of 10 °C/min. The data was collected while the oven temperature was ranging from 40 to 600 °C. Differential scanning calorimeter (DSC) measurements were carried out under N2 atmosphere using a NETZSCH DSC 200 PC analyzer. The temperature was over a range of −40 to +120 °C at a heating of 20 °C/min. Approximately 5−10 mg of PVC and self-plasticization PVC materials were weighed and sealed in a 40 μL aluminum crucible and immediately detected using DSC measurement. The DSC data was collected from a first cycle of heating. The mechanical properties including tensile modulus, tensile strength, and elongation at break were investigated according GB/T 1040.1-2006 (China) at 25 °C by using an E43.104 Universal Testing 6667


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Figure 3. Synthesis mechanism of mannich base of cardanol butyl ether.

The chemical structures of cardanol, cardanol butyl ether, and mannich base of cardanol butyl ether were also investigated by 13C NMR, and all of the peaks in the 13C NMR spectra were assigned. As seen from Figure S3, the 13C NMR chemical shifts of carbons in −O−CH2CH2CH3 and −NH−CH2−CH2−NH− groups were distinct among cardanol, cardanol butyl ether, and mannich base of cardanol butyl ether. Compared with the 13C NMR spectrum of cardanol, a new signal appeared at 66.88 ppm attributed to the carbons of the −O−CH2− groups derived from butyl chloride in the 13C NMR spectrum of cardanol butyl ether, indicating that the cardanol butyl ether was obtained. As seen from the 13C NMR spectrum of mannich base of cardanol butyl ether, these new peaks appeared in the range of 37.59−57.47 ppm, which were assigned to carbons of −NH−CH2−CH2−NH− groups derived from diethylenetriamine,40,41 indicating that the mannich base of cardanol butyl ether was obtained. The synthesis of mannich base of cardanol butyl ether experienced two steps. As seen from Figure 3, the reactive iminium ion was formed under acidic conditions in the first step. Carbonyl groups of mannich base of cardanol butyl ether were protonation in sulfuric acid solution, which was reacted with diethylenetriamine via nucleophilic addition. The electron transfer of nitrogen produced the aminocarbenium ion. The process of alkylation of the enolized carbonyl compound was produced in the second step. An enolized carbonyl compound was generated under acidic conditions. The enol structure with active hydrogen was attacked by the iminium ion as a nucleophile. Finally, the mannich base of cardanol butyl ether was obtained after losing protons. Chemical structure of PVC and self-plasticization PVC materials were investigated by FT-IR and presented in Figure 4. The peaks at 3008, 2924, 2852, 1671, 1582, 1182, 1156, 1090, and 695 cm−1 are assigned to the C−H(sp), C−H(sp3), C− H(sp2), N−H rocking vibration, CC, C−C, and N−H N−H twisting vibrations.39−41 These peaks became stronger with more displacements of chlorine atoms. In addition, the peaks at around 680 cm−1 attributed to the C−Cl24,25 appeared weak gradually with more displacements of chlorine atoms, which

Figure 4. FT-IR spectra of PVC materials.

indicated that the self-plasticization PVC materials were obtained. The chemical structures of PVC and self-plasticization PVC materials were also detected using 1H NMR, as seen from Figure 5, the peak at 4.45 ppm was attributed to protons of CH−Cl (peak A of 1H NMR spectra of PVC), and the peak at 2.06 ppm was assigned to protons of CH2 (peak B of 1H NMR spectra of PVC). A new peak appeared in the 1H NMR spectra of self-plasticization PVC materials with increasing displacement of chlorine atoms compared with 1H NMR spectra of PVC. As seen from the 1H NMR spectra of self-plasticization PVC materials (Y2 and Y4), the signals at 1.23, 3.85, 5.27, 6.58, 6.78, and 7.09 ppm were attributed to the protons of −CH2−, −NH−CH2−CH2−NH−, −CHCH−, and the benzene ring, respectively.37−41 These signals appeared stronger with more displacement of chlorine atoms, but the signal at 4.5 ppm corresponding to the protons of CH−Cl presented weaker gradually,21,22,24,25 which indicated that self-plasticization PVC materials were obtained. 6668


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Y3, and Y4, respectively. The decrease of chlorine content further illustrated that the self-plasticization PVC materials were obtained. The molecular weight and dispersity of PVC and selfplasticization PVC materials was investigated with GPC analysis, which was used to evaluate the reaction level by examining the molecular weight change.42,43 GPC spectra of PVC and self-plasticization PVC material are shown in Figure 6a. The data of number average molecular weight (Mn), weightaverage molecular weight (MW), Z-average molecular weight (MZ), and dispersity are presented in Table 1. As seen in Table 1, Mn, MW, and MZ of PVC materials increased gradually from 15 100, 18 900, and 23 000 g/mol to 24 500, 28 600, and 34 600 g/mol with increasing displacement of chlorine atoms. In addition, the GPC peak of self-plasticization PVC materials demonstrated a clear shift to the higher molecular weight region compared with that of PVC, which indicated that chlorine atoms in PVC were substituted with base of cardanol butyl ether. All self-plasticization PVC materials presented a single GPC peak with a clear shift to a higher molecular weight region, illustrating no homopolymer contamination of coupling reactions. Figure 6a shows that the peak area of selfplasticization PVC materials decreased gradually with more displacements of chlorine atoms. The reason is that highly branched self-plasticization PVC materials were filtrated by an organic membrane during the dissolution process with chromatographic purity THF as solvent.

Figure 5. 1H NMR spectra of self-plasticization PVC materials.

Chlorine content of PVC and self-plasticization PVC materials were tested using the Volhard method according to China National Standard GB/T 7139-2002 (plastic-vinyl chloride homopolymers and copolymers-determination of chlorine content). The results showed that the content of Cl was 56.5%, 42.7%, 34.3%, 25.7%, and 17.6% for PVC, Y1, Y2,

Figure 6. Characterization of chemical relative molecular mass and thermal properties. (a) GPC spectra of PVC materials; (b) DSC curves of PVC materials; (c) TGA curves of PVC materials; and (d) DTG curves of PVC materials. 6669


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1.2 1.2 1.2 1.2 1.2

Table 2. TGA, DTG, and DSC data of PVC Materials

23 000 25 600 27 500 29 700 34 600 15 100 17 900 18 900 21 000 24 500 PVC Y1 Y2 Y3 Y4

PVC materials

Td (°C)

Tp1 (°C)

Tp2 (°C)

Tg (°C)

PVC Y1 Y2 Y3 Y4

278.4 232.3 231.7 231.5 212.5

291.5 252.4 252.0 249.6 236.9

467.4 466.6 465.6 464.4 350.5

85.6 58.8 56.5 69.1 49.3

thermal degradation temperature (Td) and peak temperature of thermal degradation (Tp1 and Tp2). Thermal degradation of all PVC materials presented two stages. The first stage was assigned to dehydrochlorination of PVC. The second stage was attributed to cyclization of conjugated polyene sequences generated from dehydrochlorination of PVC and produced aromatic compounds.44−46 Table 2 shows some regular data: the characteristic temperatures of the Td, Tp1, and Tp2 for PVC decreased gradually from 278.4, 291.5, and 467.4 °C to 212.5, 236.9, and 350.5 °C with increasing substitution of chlorine atoms with mannich base of cardanol butyl ether, illustrating that the self-plasticization PVC material with active secondary amine groups was not thermally stable comparing with PVC. The internal plasticized effect of mannich base of cardanol butyl ether on PVC was detected using DSC measurements, and the glass transition temperature (Tg) is summarized in Table 2. PVC has a stiff backbone and high glass transition temperature (Tg) at around 90 °C. The addition of plasticizer into the PVC polymer will increase the distance of PVC chains and make the macromolecule structure polymer easy to move, increase the free volume of the polymer, and reduce the Tg. Substitution of chlorine atoms with mannich base of cardanol butyl ether will increase the distance between PVC chains and reduce the intermolecular force. An internal plasticization will be expected to reduce the Tg of PVC materials.47−49 As seen from Table 2 and Figure 6b, it can be found that a single change in heat capacity of Tg appeared in the DSC curves of all self-plasticization PVC materials, which illustrated that the reaction of PVC and mannich base of cardanol butyl ether was completed, and there is not any free mannich base of cardanol butyl ether that existed in the polymer. The Tg of selfplasticization PVC materials decreased from 85.6 to 49.3 °C with increasing substitution of chlorine atoms, which illustrated that mannich base of cardanol butyl ether played an internal plasticized effect on PVC. The leach tests of all self-plasticization PVC films and the 50 wt % PVC system were investigated in n-hexane at 50 °C for 2 h, and the results are shown in Figure S4. No migration was found in leaching tests for self-plasticization PVC films, but 15.7% of DOP leached from the DOP/PVC system into nhexane. The results illustrated that PVC can be plasticized in an internal plasticization way. Finally, we estimated the mechanical properties of PVC materials. As seen from Table 3, the tensile strength decreased from 30.33 to 18.86 MPa with increasing substitution of chlorine atoms with mannich base of cardanol butyl ether, and the elongation at break increased from 180.37% to 357.20%, indicating that the PVC was plasticized effectively. The mechanism of internal plasticization can be explained according to a traditional plasticization mechanism such as

18 900 21 000 22 400 24 800 28 600

no. average molecular weight (Mn, g·mol−1)

weight-average molecular weight (MW, g·mol−1)

TGA and DTG curves obtained for PVC and selfplasticization PVC materials are presented in Figure 6c,d, respectively. Table 2 summarizes the thermal data including

PVC materials

Table 1. Relative Molecular Mass and Distribution of PVC Materials

Z-average molecular weight (MZ, g·mol−1)

dispersity (MZ/MW, g·mol−1)


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plasticizer molecule, like motions in the polymer, create free volume.47,53,54 Chains of PVC with little free volume are arranged orderly and hard to move. A small intermolecular distance between chains produces a strong intermolecular force. These molecular characteristics of polymer chains make PVC present stiff and difficult to be processed. The displacement of chlorine with mannich base of cardanol butyl ether increases the distance of PVC chains and makes the macromolecule structure polymer easy to move, further increasing the free volume of polymer chains. These molecular characteristics make polymer chains of PVC present flexible and easy to be processed. However, the substituting of chlorine atoms with mannich base of cardanol butyl ether must be controlled to a certain degree, or the cross-linking of polymer with many mannich base of cardanol butyl ether chains will produce an antiplasticization effect.

Table 3. Tensile Data of PVC Materials PVC materials PVC Y1 Y2 Y3 Y4

tensile strength (MPa) 30.33 25.19 23.18 23.36 18.86

± ± ± ± ±

0.28 0.12 0.65 0.71 0.41

elongation at break (%) 180.37 237.54 288.41 330.17 357.20

± ± ± ± ±

5.16 9.10 5.10 8.10 7.92

modulus of elasticity (MPa) 153.87 ± 6.31 157.20 ± 3.01 120.54 ± 7.45 81.01 ± 4.10 75.95 ± 4.17

lubricity theory, gel theory, free volume theory, kinethic thories, and mathematical models. Figure 7 shows the internal plasticization mechanism of self-plasticization PVC materials. Mauritz and Storey developed the mathematical models for plasticization.50 Tg is an important evaluation criteria in the theory. Plasticizing efficiency at reducing Tg is based on structural features of the plasticizer such as the branchiness of the side chains and the length. For a given molecular weight, the branched plasticizer has higher plasticizing efficiency parameter values than the linear structures. In our study, selfplasticization materials with higher branchiness of the side chains and the length than PVC make self-plasticization materials become internal plasticizers. The decrease of Tg illustrated that self-plasticization materials have played a plasticizing effect on themselves. The lubricity theory was developed by Kilpatrick,47 Clark,51 and Howwink,52 among others.53 It holds that the plasticizer in PVC acts as a molecular lubricant allowing the polymer chains to move freely over one another when a force is applied to the plasticized polymer.47 Based on the theory, PVC chains do not move freely because of surfaces irregularities. As seen from Figure 7, we can conclude that mannich base of cardanol butyl ether groups of selfplasticization materials act as a solvent in the study, and the long-chain alkyl groups of self-plasticization materials act as a polymer. The structure can make the chains of selfplasticization materials move freely. The free volume theory of plasticization sought to explain the reduction in polymer glass transition temperature upon the addition of plasticizer. When plasticizer is added to the polymer, motions in the

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CONCLUSIONS With the synthesis and employment of mannich base of cardanol butyl ether, we successfully updated the method of preparing internally plasticized PVC materials using the synthesized mannich base of cardanol butyl ether as an internal plasticizer to require flexible and nonmigration PVC materials. The structure and properties of the obtained self-plasticization PVC materials were studied. The results showed that Mn, MW, and MZ of the modified PVC materials increased gradually from 15 100, 18 900, and 23 000 g/mol to 24 500, 28 600, and 34 600 g/mol with increasing displacement of chlorine; Tg decreased from 85.6 to 49.3 °C; tensile strength decreased from 30.33 to 18.86 MPa; and the elongation at break increased from 180.37% to 357.20%, indicating that mannich base of cardanol butyl ether played an internally plasticizing effect on PVC. Leaching tests show that the self-plasticization PVC materials presented excellent migration resistance compared with that of the PVC/DOP system. Therefore, we expected that the modified PVC materials can be commercial applications in producing food packing, toys, and medical devices with the high requirement in migration resistance.

Figure 7. Internal plasticization mechanism of self-plasticization PVC materials. 6671


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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.7b00900. FT-IR spectrum and 1H NMR and 13C NMR of mannich base of cardanol butyl ether; degree of migration for PVC films; formulations for synthesis of self -plasticization PVC materials. (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Puyou Jia: 0000-0002-3372-9135 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Fundamental Research Funds from Jiangsu Province Biomass and Materials Laboratory (JSBEM-S-2017010), National Natural Science Foundation of China (Grant Nos. 31670578 and 31670577), and Natural Science Foundation of Jiangsu Province of China (Grant BK20150072).

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REFERENCES

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Self-Plasticization of PVC Materials via Chemical Modification of

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